Ever since the beginning of work in the field of lithium-ion batteries by the Sony company during the early nineties, this type of batteries has been widely used, leading to a commercial success. Typically, the technology is based on the use of lithium insertion materials as electrode material. Specifically, cobalt oxide is used as cathode material (invented by J. B. Goodenough) and carbon-based materials (coke or graphitized carbon) are used as anode material.
Since then, lithium-ion batteries have progressively replaced Ni—Cd and Ni-MH batteries. Indeed in many electronic applications, lithium-ion batteries perform better than Ni—Cd and Ni-MH batteries. However, because the production cost of lithium-ion batteries is high and because their intrinsic stability is generally compromised under harsh conditions, only small format lithium-ion batteries have been successfully commercialized.
Today the technology is based mostly on the use of anode materials containing graphite. However, it appears that the use of such carbon-based anode imposes a 372 mAh/g limit for the specific energy capacity, with no possibility of further increase.
The use of metallic lithium as anode material has been investigated. Indeed, metallic lithium presents a high energy density and may lead to a high specific energy capacity. However, security issues are associated to the use of metallic lithium. This is due to the growth of dendrites during use. Moreover, a limit on the lifetime after many charge/discharge cycles has been noted. These disadvantages have caused researchers to look for other solutions. For example, the use of silicon (Si), tin (Sn) and their alloys as potential high capacity anode materials has been investigated.
Indeed regarding silicon, this metal allows for a reversible insertion and de-insertion of lithium ions through a reaction between silicon and lithium, 5Si+22Li→Si5Li22, which corresponds to a theoretical capacity of 4200 mAh/g. This capacity is significantly higher than the capacity for carbon-based materials. However, silicon-based anodes are unstable during cycling due to the high volume expansion of silicon (up to about 320%).
Reducing the particle size of a silicon-based anode material (use of nanoscale particles for example) leads to better cycling performance. Indeed, the use of nanoscale particles allows for the relaxation of internal mechanical constraints associated to the large volume increase [1]. A technique consists of using a material which has a nanoscale filament structure. Indeed, such structure can accommodate the deformations in the radial direction of fibers, thus avoiding pulverization of silicon and loss of electric contacts [1,2].
Another technique for decreasing the volume expansion consists of preparing an intimate mixture of silicon and an inert component that can accommodate the deformation. For example, a fine dispersion of silicon in an inactive matrix which relaxes mechanical constraints and insures electric continuity has been prepared [1,3]. Such compromise may be achieved by using a mixture of Si/SiO2, at the expense of a partial loss of silicon capacity. In this regard, the use of silicon monoxide (SiOx, with x≈1) that has been annealed, allows for a dismutation reaction, 2SiO→SiO2+Si. The amorphous phase of SiOx outside the reaction equilibrium precipitates silicon in an amorphous SiO2 matrix, which leads to a material having a theoretical capacity of 1338 mAh/g [4].
The first synthesis of SiOx was performed by Potter in 1907 [5]. Potter noted that at temperatures higher than 1000° C., a rapid reaction between silicon (Si) and silicon oxide (SiO2) occurs. He further noted that if the reaction occurs under inert atmosphere, the reaction product appears as a brown, light, very fine and voluminous powder.
SiOx is currently commercially available. It is produced at a moderately high temperature (about 1250° C.), under vacuum, according to the following reaction [6]:

An equimolar mixture of SiO2 powder and Si powder in a tube is heated, under vacuum, until a temperature of 1250° C. is reached. Gaseous SiO formed is directed to an area of the tube that is colder and is condensed. The tube is cooled, re-pressurized, and solid SiOx is recuperated. The solid SiOx is then submitted to a grinding process until the desired granulometry is reached.
The relatively low temperature of the process, about 1250° C., allows for the use of a vacuum tube made in stainless steel (retort furnace). However in return, the partial pressure of gaseous SiO in the tube is maintained at a very low level, which greatly affects the productivity of the process. A micrograph taken by a scanning electron microscope shows a typical aspect of the material (FIG. 1) through its X-ray diffraction analysis. The X-ray diffraction analysis shows the amorphous nature of the material. Indeed, no diffraction pic is observed. This is typical to amorphous SiO that has been cooled rapidly and that has not undergone any dismutation reaction.
It is known that annealing such material at a temperature higher than 900° C., under inert atmosphere, does activate the dismutation reaction of SiO, which leads to the precipitation of a very fine silicon phase in an amorphous silicon matrix [3]:

Indeed, Takami et al. [3] prepared a composite of Si, SiOx and C by dismutation of silicon monoxide and polymerization of furfurylic acid at 1000° C. They reported a reversible capacity of about 700 mAh/g for 200 cycles.
There is still a need for materials having a high energy capacity; advantageously, the capacity is reversible for a high number of cycles. Accordingly, there is also a need for processes for preparing these materials; advantageously, the process is efficient and cost-effective.
A material having a high energy capacity can be a nanometric dispersion of crystalline Si in an amorphous SiO2 matrix. Lamontagne et al. disclose a process for the preparation of such material. The process uses SiO2 fume; also the process involves uses of various catalysts [7].
Encouraged by the result obtained by Takami et al. relative to a composite of Si, SiOx and C [3], our research group took up a more close investigation of the use of SiOx as electrode material in Li-ion batteries. We have studied, respectively, the use of SiOx and SiOx mixed with graphite as anode material in lithium-ion batteries [4]. Despite the fact that the coulombic efficiency of the first charge/discharge cycle and the electronic conductivity of SiOx are low, the theoretical specific capacity of SiOx electrodes is good, 1338 mAh/g. We have considered the addition of graphite to SiOx.